Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.
OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.
One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.
One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)3, which has the following structure:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.
As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.
As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.
As used herein, “solution processable” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.
A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.
As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.
As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.
More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.
In a typical bottom-emission OLED device, the anode material is conventionally a transparent conducting oxide (TCO), which generates power losses and Joule heating due to its relatively high resistivity and thin film thickness. For example, sheet resistance is typically in the range of 10-100 Ohm/square for a thickness range of 50-200 nm. This is in contrast to metal, which is often used for the reflective cathode. This can result in brightness non-uniformity, which becomes more evident when scaling up to large-area light panels. In order to improve uniformity, highly-conductive metal bus lines may be deposited in electrical contact with the TCO electrode to provide improved current distribution across the panel. Bus lines can help distribute current more evenly across the entire panel with very little power loss. A similar approach may be applied to top-emission OLED devices, where a semi-transparent cathode is required. In this instance, uniformity may be improved by depositing highly conductive metal bus lines in electrical contact with the cathode. In a transparent OLED device, highly conductive metal bus lines may be deposited in electrical contact with both electrodes.
The conventional way to pattern metal bus lines is through photolithography followed by a lift-off process. Many published materials have taught that an insulating layer (such as SiO2 or a photo-resist) is required to cover the bus lines to prevent shorting. U.S. Patent Application Pub. No. US 2003/0006697 by Weaver discloses such a device including a first electrode, an insulating strip disposed over a portion of the first electrode, and a bus line disposed on top of the insulating strip, such that the bus line is electrically insulated from the first electrode by the insulating strip. International Patent Application Pub. No. WO 2010/038181 A1 by Schwab et al. (“Schwab”) also describes an OLED device where bus (shunt) lines are applied to an electrode. Schwab goes on to describe how passivation (electrical insulation) at least partially and preferably totally covering the bus lines is required to prevent electrical shorting to an opposing electrode. In fact, it has become a standard practice in the industry to use an insulating layer (e.g., SiO2, SiN, polyimide etc.) to cover the bus lines to prevent electrical shorts occurring between the bus lines and the opposing electrode.
However, introducing an insulating layer, or grid, such as those described in the foregoing publications, can reduce the emissive area since the area covered by the insulating material is non-emissive. In addition, shelf life of the OLED may be reduced if moisture is stored in the insulating layer. Finally, bus lines and the insulating layer are typically patterned using photolithography, which is time-consuming and expensive.